Design and Examination of Compound Planetary Gearboxes to Investigate the Impact of 3D-Printed Embedded Bearings for Assistive Exoskeletons Actuators

Abstract In robotic systems such as wearable exoskeletons, lightweight, efficient, and backdrivable reduction gearboxes are critical for achieving low-output impedance actuators and safe physical human-robot interaction. Recent trends in robotics research highlight the growing adoption of 3D-printed gearboxes, which enable rapid prototyping, flexibility, and lightweight solutions. However, these reducers can still exhibit significant weight and encumbrance, mainly due to the reliance on conventional bearings that add substantial bulk and mass. In this paper, we design and experimentally evaluate two 3D-printed 1:30 compound planetary reducers. The first prototype employs standard bearings, while the second integrates 3D-printed bearing guides composed of steel rollers moving through custom polymer raceways embedded in the gearbox components. This approach aims at diminishing the reducer's overall cost, weight, and encumbrance, while retaining key mechanical performance characteristics. Experimental results show that the proposed 3D-printed bearing solution reduces gearbox weight by approximately 32% and manufacturing cost by about 33% compared to the bearing-based counterpart. Moreover, the reducer achieves a backdrive torque as low as 0.42 ± 0.06 Nm, representing the lowest value among the compared designs, together with a marked reduction in internal friction. Despite the replacement of conventional bearings with fully integrated printed guides, the gearbox preserves comparable gear play and stiffness while improving backdriveability and speed regularity. These results demonstrate that fully customized, additively manufactured reducers with embedded bearing systems can provide substantial mechanical and integration advantages for lightweight wearable robotic actuators.